Photodegradable polyolefins containing nitrohaloalkanes

ABSTRACT

Polyolefins capable of photodegradation are prepared by incorporating in the polyolefin an additive containing chlorine, bromine, or iodine and either a nitrogen or a sulfur group.

This is a division of our copending application Ser. No. 603,080, filedAug. 8, 1975, now U.S. Pat. No. 3,968,096, which in turn is a divisionof our prior application, Ser. No. 543,706, filed Jan. 23, 1975, nowU.S. Pat. No. 3,929,723.

DESCRIPTION OF THE INVENTION

The invention relates to and has among its objects the provision ofnovel plastic compositions capable of photodegradation. Further objectsof the invention will be evident from the following description whereinparts and percentages are by weight unless otherwise specified.

Plastics have become an important part of the American way of life.Innumerable articles of manufacture are made of plastics. One of themain uses thereof is in the manufacture of containers for liquids andsolids of all kinds, particularly foods. Another important use is themanufacture of plastic sheet materials such as films and foils. Forexample, plastic films are used in agriculture for covering the soilbetween plants, thereby to prevent the growth of weeds.

One problem with plastics is that they are not easily decomposed. Thus,for example, plastic food containers thrown by the roadside do notdecompose but remain until collected, thereby polluting the environment.Similarly, plastic films used as soil coverings must be removed from thefields prior to initiating a new crop.

The invention described herein concerns a means for obviating the aboveproblems in that it provides polyolefin plastics which are capable ofphotodegradation. Containers fabricated from the plastics of theinvention when exposed to sunlight will gradually decompose andeventually crumble away. Thus, such containers when thrown along theroadside will eventually become part of the soil. Films prepared fromthe plastics of the invention when used for agricultural purposes willgradually become friable by the action of sunlight so that they can bereadily plowed into the soil.

The benefits of the invention are realized by incorporating into apolyolefin any of the compounds described below.

Group I. Cyanohalomethanes of the structure

    C(CN).sub.r X.sub.q

Wherein:

X is chlorine, bromine, or iodine

R IS 1, 2, OR 3

Q IS 4-R

Illustrative examples of compounds included in Group I are:

Trichloroacetonitrile

Tribromoacetonitrile

Triiodoacetonitrile

Dichloromalononitrile

Dibromomalononitrile

Diiodomalononitrile

Chlorotricyanomethane

Bromotricyanomethane

Iodotricyanomethane

Group II. Nitrobenzenesulfenyl halides of the structure ##STR1##WHEREIN:

X is chlorine, bromine, or iodine

N IS 1 OR 2

Illustrative examples of compounds included in Group II are:

2,4-Dinitrobenzenesulfenyl chloride

2,4-Dinitrobenzenesulfenyl bromide

2,4-Dinitrobenzenesulfenyl iodide

Group III. Haloalkylsulfenyl halides of the structure

    X--S--(CH.sub.b X.sub.a).sub.c --R

wherein:

X is chlorine, bromine, or iodine

R is hydrogen, chlorine, bromine, iodine, or an alkyl radical containing1 to 6 carbon atoms

a is 1 or 2

b is 2-a

c is 1 or 2

Illustrative examples of compounds included in Group III are:

Trichloromethylsulfenyl chloride

Tribromomethylsulfenyl chloride

Triiodomethylsulfenyl chloride

Trichloromethylsulfenyl bromide

Trichloromethylsulfenyl iodide

Tribromomethylsulfenyl bromide

Tribromomethylsulfenyl iodide

Triiodomethylsulfenyl bromide

Triiodomethylsulfenyl iodide

1,1,2,2-Tetrachloroethylsulfenyl chloride

1,1,2,2-Tetrachloroethylsulfenyl bromide

1,1,2,2-Tetrachloroethylsulfenyl iodide

1,1,2,2-Tetrabromoethylsulfenyl chloride

1,1,2,2-Tetrabromoethylsulfenyl bromide

1,1,2,2-Tetrabromoethylsulfenyl iodide

1,1,2,2-Tetraiodoethylsulfenyl chloride

1,1,2,2- Tetraiodoethylsulfenyl bromide

1,1,2,2-Tetraiodoethylsulfenyl iodide

Group IV. Halobenzenesulfonyl halides of the structure ##STR2## wherein:

X is chlorine, bromine, or iodine

p is an integer from 1 to 5

Illustrative examples of compounds included in Group IV are:

2-Chlorobenzenesulfonyl chloride

2-Chlorobenzenesulfonyl bromide

2-Chlorobenzenesulfonyl iodide

2,4,5-Trichlorobenzenesulfonyl chloride

2,4,5-Trichlorobenzenesulfonyl bromide

2,4,5-Trichlorobenzenesulfonyl iodide

Pentabromobenzenesulfonyl chloride

Pentabromobenzenesulfonyl bromide

Pentabromobenzenesulfonyl iodide

Group V. Haloalkylsulfonyl halides of the structure

    X--SO.sub.2 --(CH.sub.b X.sub.a).sub.c --R

wherein:

X is chlorine, bromine, or iodine

R is hydrogen, chlorine, bromine, iodine, or an alkyl radical containing1 to 6 carbon atoms

a is 1 or 2

b is 2-a

c is 1 or 2

Illustrative examples of compounds included in Group V are:

Trichloromethanesulfonyl chloride

Tribromomethanesulfonyl chloride

Triiodomethanesulfonyl chloride

Trichloromethanesulfonyl bromide

Trichloromethanesulfonyl iodide

Tribromoethanesulfonyl bromide

Tribromomethanesulfonyl iodide

Triiodomethanesulfonyl bromide

Triiodomethanesulfonyl iodide

1,1,2,2-Tetrachloroethanesulfonyl chloride

1,1,2,2-Tetrachloroethanesulfonyl bromide

1,1,2,2-Tetrachloroethanesulfonyl iodide

1,1,2,2-Tetrabromoethanesulfonyl chloride

1,1,2,2- Tetrabromoethanesulfonyl bromide

1,1,2,2-Tetrabromoethanesulfonyl iodide

1,1,2,2-Tetraiodoethanesulfonyl chloride

1,1,2,2-Tetraiodoethanesulfonyl bromide

1,1,2,2-Tetraiodoethanesulfonyl iodide

Group VI. Haloalkyl disulfides of the structure

    R--(CH.sub.b X.sub.a).sub.c --S--S--(CH.sub.b X.sub.a).sub.c --R

wherein:

X is chlorine, bromine, or iodine

a is 1 or 2

b is 2-a

c is 1 or 2

R is hydrogen, chlorine, bromine, iodine, or an alkyl radical containing1 to 6 carbon atoms

Illustrative examples of compounds included in Group VI are:

Bis-(trichloromethyl) disulfide

Bis-(tribromoethyl) disulfide

Bis-(triiodomethyl) disulfide

Bis-(1,2,2,2-tetrachloroethyl) disulfide

Bis-(1,2,2,2-tetrabromoethyl) disulfide

Bis-(1,2,2,2-tetraiodoethyl) disulfide

Bis-(1,1,2,2-tetrachloroethyl) disulfide

Bis-(1,1,2,2-tetrabromoethyl) disulfide

Bis-(1,1,2,2-tetraiodoethyl) disulfide

Group VII. Halonitroalkanes of the structure

    O.sub.2 N--(CH.sub.b X.sub.a).sub.c --R

wherein:

X is chlorine, bromine, or iodine

R is hydrogen, chlorine, bromine, iodine, or an alkyl radical containing1 to 6 carbon atoms

a is 1 or 2

b is 2-a

c is 1 or 2

Illustrative examples of compounds included in Group VII are:

Chloropicrin

Bromopicrin

Iodopicrin

Perchloronitroethane

Perbromonitroethane

Periodonitroethane

Polyolefins containing any of the above compounds (or additives as theyare often referred to herein) decompose readily when exposed tosunlight. The decomposition, however, is not instantaneous but isgradual, and the rate thereof depends on such factors as the type ofpolyolefin, the amount of the compound added, and the activity of thelatter. The reaction which takes place can be described as aphotodepolymerization in which the polymeric chains are reduced to lowermolecular weight under the influence of sunlight.

The amount of additive to be incorporated with the polyolefin depends onthe activity of the additive, and upon the desired rate ofphotodecomposition. In general, one may use about 0.1 to 10% of theadditive, based upon the weight of polyolefin. For most purposes, about1 to 5% of the additive is sufficient to obtain a reasonable and usefulrate of photodegradation.

The polyolefin to which the invention is applied includes, for example,high and low density polyethylene, polypropylene, polybutylene,polystyrene, mixtures of polyethylene and polypropylene, vinylacetate/ethylene copolymers, and the like. The incorporation of theadditive with the polyolefin may be carried out in any of the ways knownin the art of compounding plastics. For example, intimate mixing of thepolyolefin and additive may be effected by melting and mixing thepolyolefin with the additive by any suitable means such as a mixer ofthe Banbury or Werner type or in a screw extruder. The compositions ofpolyolefin and additive can be formed into any desired articles such asfilms, tubular sheets, foils, bags, bottles, or other containers byapplication of well-known molding and fabricating techniques.

It is within the compass of the invention to use known photosensitizingcompounds such as dibenzoyl peroxide, azo-bis-isobutyronitrile, and thelike in conjunction with the additives of the invention. In someinstances such photosensitizers increase the activity of the additivesof the invention. Thus, polyolefins containing an additive in accordancewith the invention and a photosensitizer will exhibit an enhanced rateof photodegradation.

EXAMPLES

The invention is further demonstrated by the following illustrativeexamples.

EXAMPLE 1 Photodegradable Polypropylene Films

A. To 0.6 gram of powdered polypropylene resin was added a solution of0.006 gram of additive in 0.6 ml. of acetone. The mixture was stirred toevenly distribute the additive solution over the particles ofpolypropylene. The mixture was spread as a thin layer on a Mylar sheetsupported by a ferrotype chrome plate. After allowing the acetone toevaporate, the said layer was covered with another Mylar sheet andchrome plate. This assembly was heated for 30 sec. at 350° F. and thenpressed at 370 psi. for 30 sec. The assembly was then transferred to anunheated press and pressed at 4000 psi. while cooling. A film ofpolypropylene and 1% additive having a thickness of 0.003 to 0.004 inchwas thus obtained.

A similar procedure was employed for the preparation of polypropylenefilms containing other additives. In cases wherein the melting point ofthe additive was above 350° F., the temperature of the press wasmaintained at about 10° F. above this melting point and within the rangeof 350°-412° F. A piece, 3/4 inch × 13/8 inches, was cut from each filmand its infrared spectrum was taken.

B. Test procedure: The films prepared as above described were placed ina stainless steel rack exposed to sunlight. This rack was mounted on abuilding located at Albany, California, and was positioned facing southand at an angle of 45° to the horizontal. The films were thus exposedcontinuously for a period of approximately one month, that is, fromSept. 14 to Oct. 11 of one calendar year. After this exposure, aninfrared spectrum of the sample was again determined. The extent ofphotooxidation was taken as a measure of the photodegradability of theirradiated material. Photooxidation was determined by measuring theincrease in the carbonyl absorption band of the exposed sample over thatof an irradiated sample containing no additive.

C. Specific additives used: The sequence described above in parts A andB was performed with the following additives, each in the amount of from3 to 5%, based on the weight of polypropylene:

    __________________________________________________________________________    a.                                                                              Dibromomalononitrile  Br.sub.2 C(CN).sub.2                                  b.                                                                              Trichloromethanesulfonyl chloride                                                                   ClSO.sub.2CCl.sub.3                                   c.                                                                              2,4,5-Trichlorobenzenesulfonyl chloride                                                              ##STR3##                                             d.                                                                              Chloropicrin          O.sub.2 NCCl.sub.3                                    e.                                                                              1,1,2,2-Tetrachloroethylsulfenyl chloride                                                            ##STR4##                                             f.                                                                              Bis-(1,2,2,2-tetrachloroethyl) disulfide                                                            Cl.sub.3 CCH(Cl)SSCH(Cl)CCl.sub.3                     __________________________________________________________________________     The results are summarized below.                                        

                                      Table 1                                     __________________________________________________________________________    Polypropylene and Additive                                                    __________________________________________________________________________                                       Increase in                                                                           Additive                                                       Amount of                                                                            carbonyl, ab-                                                                         effectiveness                      Run  Additive               additive, %                                                                          sorbance units                                                                        ratio*                             __________________________________________________________________________    a.   Dibromomalononitrile   3      0.234   31.2                               b.   Trichloromethanesulfonyl chloride                                                                    3      0.044   5.9                                c.   2,4,5-Trichlorobenzenesulfonyl chloride                                                              5      0.158   21.1                               d.   Chloropicrin           5      0.023   3.1                                e.   1,1,2,2-Tetrachloroethylsulfenyl chloride                                                            5      0.175   23.3                               f.   Bis-(1,2,2,2-Tetrachloroethyl) disulfide                                                             5      0.031   4.1                                Control                                                                              None used                   0.008   1.0                                __________________________________________________________________________      *Additive effectiveness ratio is equal to the increase in carbonyl for a     particular additive divided by the increase in carbonyl obtained without      additive (control). Thus, for example, polypropylene containing               dibromomalononitrile is oxidized photochemically 0.234/0.008 or 31.2 time     more than polypropylene without an additive.                             

EXAMPLE 2 Photodegradable Polyethylene Films

Polyethylene films containing 2 to 5% of additive were prepared by thesame procedure described in Example 1. Photodegradability of theresulting films was determined as described in Example 1.

    __________________________________________________________________________    The following additives were used:                                            Runs a to f: Same additives as Example 1                                      __________________________________________________________________________    g.                                                                              Trichloromethylsulfenyl chloride                                                                  ClSCCl.sub.3                                            h.                                                                              2,4-Dinitrobenzenesulfenyl chloride                                                                ##STR5##                                               __________________________________________________________________________     The results are summarized below.                                        

                                      Table 2                                     __________________________________________________________________________    Polyethylene and Additive                                                     __________________________________________________________________________                                        Increase in                                                                           Additive                                                      Amount of                                                                             carbonyl, ab-                                                                         effectiveness                     Run  Additive               additive, %                                                                           sorbance units                                                                        ratio                             __________________________________________________________________________    a.   Dibromomalononitrile   5       0.056   4.3                               b.   Trichloromethanesulfonyl chloride                                                                    5       0.021   1.6                               c.   2,4,5-Trichlorobenzenesulfonyl chloride                                                              5       0.052   4.0                               d.   Chloropicrin           5       0.037   2.8                               e.   1,1,2,2-Tetrachloroethylsulfenyl chloride                                                            5       0.071   5.5                               f.   Bis-(1,2,2,2-tetrachloroethyl) disulfide                                                             5       0.067   5.2                               g.   Trichloromethylsulfenyl chloride                                                                     2       0.021   1.6                               h.   2,4-Dinitrobenzenesulfenyl chloride                                                                  5       0.020   1.5                               Control                                                                            None used                      0.013   1.0                               __________________________________________________________________________

EXAMPLE 3 Photodegradable Polystyrene Films

A. Commercial polystyrene powder was first purified as follows: Thepowder (90 g.) was placed in a 2-liter Erlenmeyer flask together with510 ml. of chloroform and the mixture was shaken until dissolved. Thesolution was poured slowly with vigorous stirring into a one-gallonWaring Blender containing 2 liters of methanol. The finely precipitatedpowder was filtered, washed with methanol, air-dried, and finally driedin a vacuum oven at 52° C. and 30 p.s.i. This procedure was repeated fora total of three times and a polystyrene containing no styrene odor wasobtained.

B. Incorporation of additive: A wide-mouth jar was charged with 3 g. ofthe purified polystyrene powder, 0.15 g. of additive, and 17 ml. ofchloroform, then shaken on a wrist-action shaker until solution wasobtained. The solution was allowed to stand for a few minutes to removeentrapped air bubbles. Afterward, the solution was spread on a 4 × 8inch glass plate with a film-casting knife with a setting of 0.038 inch.The plate was suspended above chloroform in a covered tray to retardevaporation of the solvent. After the plate had dried overnight, it wasplaced in a tray containing distilled water, which floated the film awayfrom the glass. This film of polystyrene plus the incorporated additivewas about 0.004 to 0.005 inch thick. A piece, 3/4 inch × 13/8 inches wascut from the film and its infrared spectrum was taken.

C. Test procedure: The said piece of film was then irradiated for 66hours by maintaining it on a revolving table 9 in. in diameter with thefilm sample 6 in. from a 275-watt RS sunlamp. After irradiation, aninfrared spectrum of the sample was again determined. The extent ofphotooxidation was taken as a measure of the photodegradability of theirradiated material. Photooxidation was determined by measuring theincrease in the carbonyl absorption band of the irradiated sample overthat of an irradiated sample containing no additive.

D. Specific additives used: The sequence described above in parts A, B,and C was performed with all of the additives mentioned in Example 2.

The results are tabulated below:

                                      Table 3                                     __________________________________________________________________________    Polystyrene and Additive                                                      __________________________________________________________________________                                        Increase in                                                                           Additive                                                      Amount of                                                                             carbonyl, ab-                                                                         effectiveness                     Run  Additive               additive, %                                                                           sorbance units                                                                        ratio                             __________________________________________________________________________    a.   Dibromomalononitrile   5       0.334   3.0                               b.   Trichloromethanesulfonyl chloride                                                                    5       1.012   9.0                               c.   2,4,5-Trichlorobenzenesulfonyl chloride                                                              5       0.735   6.6                               d.   Chloropicrin           5       0.137   1.2                               e.   1,1,2,2-Tetrachloroethylsulfenyl chloride                                                            5       0.414   3.7                               f.   Bis-(1,2,2,2-tetrachloroethyl) disulfide                                                             5       0.510   4.6                               g.   Trichloromethylsulfenyl chloride                                                                     3       0.422   3.8                               h.   2,4-Dinitrobenzenesulfonyl chloride                                                                  5       0.227   2.0                               Control                                                                            None used                      0.112   1.0                               __________________________________________________________________________

Having thus described our invention, we claim:
 1. A photodegradablecomposition comprising a polyolefin and about from 0.1 to 10%, based onthe weight of polyolefin, of an additive of the structure

    O.sub.2 N--(CH.sub.b X.sub.a).sub.c --R

wherein: X is chlorine, bromine, or iodine R is hydrogen, chlorine,bromine, iodine, or an alkyl radical containing 1 to 6 carbon atomsa is1 or 2 b is 2-a c is 1 or
 2. 2. The composition of claim 1 wherein theadditive is chloropicrin.